In general, RF communication systems and devices, like other electronics, require testing and, in some cases, calibration. Testing and calibration can present challenges in the case of an RF communication system or device which supports multiple transmission (Tx) and reception (Rx) channels.
Some traditional approaches use a single-channel measurement instrument to test and calibrate each channel of a multi-channel RF communication device individually, one-by-one, in sequence. However, these approaches have some drawbacks. First, the repeated connection and disconnection of the single-channel measurement instrument to the multi-channel RF communication device under test (DUT) using RF connectors will influence the testing accuracy and repeatability. Second, as the number of transmission and/or reception channels increases, the time required to perform test and calibration also increases. In particular, in the case of massive multi-input, multi-output (MIMO) communication systems which are now being developed, the number of channels is very large (in many cases more than 64) and as a result testing each of these channels one-by-one is very time consuming and in fact as the number of channels increases, the time required can be prohibitive.
Some other approaches use multiple test instruments, or a multi-channel test instrument, to test channels in parallel. However, a disadvantage of this approach is that when the number of channels is very large, the test instruments, or multi-channel test instrument, becomes too expensive and even impractical.
Antenna array test and calibration approaches are widely used in both aerospace defense industry and also the wireless communication industry. Typical approaches mostly utilize a vector network analyzer and require the DUT to have RF connectors for the test. With the development of wireless communication technologies, the remote radio unit (RRU) and the baseband processing unit (BBU) are more often connected with a digital fiber interface, for example the Common Public Radio Interface (CPRI). CPRI is an example of an internal interface of a radio base station which links a radio equipment portion of the radio base station to a radio equipment control portion of the base station. CPRI is described in the CPRI Specification Version 5.0 or 6.0, for example. Other digital interfaces can also be used.
With such digital fiber interfaces, the prior antenna array test and calibration approaches are no longer applicable. New test and calibration methods for digital antenna arrays are needed. With the wireless communication technology moving toward the use of 5G, massive MIMO technology is going to be used. The digital massive MIMO antenna arrays bring the test and measurement challenges from not only the interface part, but also the overall test approach scalability, the test speed, the test calibration for broadband modulated signals etc.
Thus, the existing test approaches cannot provide a suitable test system and method that has a fast testing speed and low cost for future massive MIMO systems. It would be desirable to provide a more convenient (e.g. faster testing speed and lower cost) and more reliable method and system to test and calibrate the performance of a multi-channel RF communication system or device.